Taylor Swift Joined by Ellie Goulding on Final Night of Red Tour [VIDEO]

Last night (Feb. 11) at London's O2 Arena, the British singer sang her single 'Burn' with vocal -- and dancing! -- accompaniment from Taylor. The pair, wearing similar high-waisted shorts, appear to be having a blast as they lead the crowd in singing along and holding their cellphones aloft. Ellie was also one of the many artists Taylor brought on stage during her stand at L.A.'s Staples Center last year. They sang Ellie's 'Anything Could Happen' that evening.

Both artists, who both have admitted girl crushes on the other, later posted the same Polaroid picture of them posing together -- and showing off Taylor's new haircut!

Taylor wrote, "London, I could never thank you enough. See you next time! PS: short hair, don't care. (!!!)" Ellie captioned it, "Had the most fun. Beautiful person inside and out @taylorswift love ya"

Ellie shared another photo of them, along with model Cara Delevingne, writing, "Just some dorks. And a stellar haircut"

Last night was the final show of Taylor's tour, which kicked off in March 2013 and traveled around the world. It was also the final night of Taylor's five-night stand at the O2. On Monday (Feb. 10), she was joined by Emeli Sande for a duet on Emeli's 'Next to You.' Prior shows at the arena included appearances by guests invited (Ed Sheeran and Sam Smith) and definitely not invited (a fan who bum-rushed the stage).